The Gemara tells us there is no reward for mitzvos in this world. Yet, we see Chazal tell us (all the time) that in the zchus of certain actions (like not changing our names in Mitzrayim and other actions) we were saved from Egypt. Or in the zchus of doing certain mitzvos, hashem seemingly rewarded us. How can one understand these sources? Also, people do segulas or even do certain mitzvos today in order to try to get their desires answered from Hashem instead of davening directly to Hashem. Shouldn’t mitzvot be used to serve Hashem and not to gain personal desires out of doing mitzvos.
Although Rabbi Yaakov (Kiddushin 39b) states that there is no reward for mitzvos in this world, this statement cannot be taken entirely literally, for we find explicit verses promising reward in this world (such as in the second paragraph of the Shema), and we find throughout the Torah that good was rewarded and bad was punished — in this world — as we say in davening: “On account of our sins we were exiled from our Land.”
There are several approaches that come to resolve this seeming contradiction. Some say that there is a difference between the community and single people (Maharsha). The Maharit writes that the opinion of Rabbi Yaakov refers only to a case in which a person requires a miracle: According to Rabbi Yaakov Hashem will not take away one’s reward for the World to Come by making a miracle here. See also the Rambam (Teshuvah 9:1) who makes a distinction between the principle reward in the World to Come, and a certain reward here.
Either way, there is no doubt that a person is rewarded even in this world, and according to the Ramban (end of Bo) it is one of the fundamentals of our faith to believe that whatever overcomes us is factor of our own deeds: The good that overcomes us is a factor of our good deeds, and the bad a factor of our negative deeds.
The Gemara also states that a person who gives charity and says that it should be for the zechus of his sick child, is still considered wholly righteous.The reason why this remains righteous is that it refers to somebody who would anyway have done the mitzvah — and means to do it as service of Hashem — but wishes to dedicate the merit of the mitzvah for a particular purpose.
There matters are of course far deeper than this short answer, but I hope it nonetheless goes some small way towards clarification.